AXOLOTL. MENOBRANCHUS. 189 



been completely calcified and converted into hard dentine, the corres- 

 pondence between the siren and the lepidosiren would have been 

 very striking in this part of their structure ; but the maxillary 

 sheaths of the siren being composed of horn, and being, moreover, 

 easily detached from the subjacent bones, much more closely resem- 

 ble the deciduous mandibles of the tadpoles of the higher Batra- 

 chians.(l) 



77. Axolotl.-— The ichthyic character of rasp-like teeth, aggregated 

 in numerous series, is manifested also in the Axolotl upon the palatal 

 region of the mouth, and upon the splenial or opercular element of 

 the lower jaw ; but the superior maxillary bones are here developed and 

 support teeth (PI. 62, fig. 4). The premandibular and the inter- 

 maxillary bones (a) , instead of presenting the larval condition of the 

 horny sheath, have their alveolar border armed with a single row of 

 small, equal, fine, and sharp pointed denticles, which are continued 

 above, along the maxillaries (&) ; thus establishing the commencement 

 of the ordinary batrachian condition of the marginal teeth of the buccal 

 cavity. The dentigerous bones of the palate consist of two plates on 

 each side, as in the siren ; the anterior pair, or vomers, (c), converge 

 and meet at their anterior extremities ; the minute denticles which they 

 support are arranged quincuncially : the posterior pair of bones, (d), are 

 continued backwards, according to the usual disposition of the ptery- 

 goids, to abut against the tympanic or quadrate bones ; the denticles are 

 confined to the anterior part of their oral surface and resemble in their 

 arrangement and anchylosed attachment those of the palatal series of 

 which they form the posterior termination. 



78. Menobranchus. — Although in this genus the superior maxillaries 

 and their teeth are wanting, an advance to a higher type of dentition 



(1) " Leur bord est tranchant et garni dans I'animal frais d'une gaine presque cornee, qui 

 se detache aisement de la gencive, et qui a son analogue dans les tetards de grenouille." — 

 Cuvier, Ossem. Foss. Ed. 1837, x, p. 341. The combination of trenchant with lacerating 

 rasp-like dental instruments in the jaws of the Siren was recognized by Ellis, who has given 

 a figure of them in the 56th volume of the Philosophical Transactions, Pi. IX. c. He says, 

 "The mouth is small in proportion to the body; but its palate and inside of the lower jaw 

 are well provided with many rows of pointed teeth ; with this provision of nature, added to 

 the sharp exterior bony edges of both the upper and under jaw, the animal seems capable of 

 biting and grinding the hardest kind of food." 



